Interaction of Synthetic D-6-deoxy-myo-inositol 1,4,5-trisphosphate with the Ca2(+)-releasing D-myo-inositol 1,4,5-trisphosphate Receptor, and the Metabolic Enzymes 5-phosphatase and 3-kinase

The ability of D-6-deoxy-myo-inositol 1,4,5-trisphosphate [6-deoxy-Ins(1,4,5)P3], a synthetic analogue of the second messenger D-myo-inositol 1,4,5-trisphosphate [Ins(1,4,5)P3], to mobilise intracellular Ca2+ stores in permeabilised SH-SY5Y neuroblastoma cells was investigated. 6-Deoxy-Ins(1,4,5)P3 was a full agonist (EC50 = 6.4 microM), but was some 70-fold less potent than Ins (1,4,5)P3 (EC50 = 0.09 microM), indicating that the 6-hydroxyl group of Ins(1,4,5)P3 is important for receptor binding and stimulation of Ca2+ release, but is not an essential structural feature. 6-Deoxy-Ins(1,4,5)P3 was not a substrate for Ins (1,4,5)P3 5-phosphatase, but inhibited both the hydrolysis of 5-[32P]+ Ins (1,4,5)P3 (Ki 76 microM) and the phosphorylation of [3H]Ins(1,4,5)P3 (apparent Ki 5.7 microM). 6-Deoxy-Ins (1,4,5)P3 mobilized Ca2+ with different kinetics to Ins(1,4,5)P3, indicating that it is probably a substrate for Ins (1,4,5)P3 3-kinase.